Various types of lockdown sleeves (LDS) have been conceived for axially interconnecting a casing hanger and a subsea wellhead. In some applications, no seal between the casing hanger and the wellhead is provided by the lockdown sleeve. In other applications, a lockdown sleeve may be designed to seal with the casing hanger. Even when a lockdown sleeve is provided, a single seal is conventionally used to seal the annulus between the wellhead and the casing hanger.
Prior art patents include U.S. Pat. No. 5,273,117 which discloses a locking ring for locking an outer wellhead housing to an inner wellhead housing. U.S. Pat. No. 5,287,925 discloses multiple seals with the wellhead housing. U.S. Pat. No. 7,219,738 discloses a locking member and a seal between the wellhead and a seal body.
The disadvantages of the prior art are overcome by the present invention, and an improved casing hanger lockdown sleeve, running tool, and method of locking down and sealing a casing hanger to a wellhead are hereinafter disclosed.